Flame resistant resin compositions

ABSTRACT

Diallyl maleate in combination with triethyl phosphate, when added to styrene-unsaturated polyester resin systems and cured with a free-radical forming initiator provides a high level of flame resistance.

The present invention is a continuation-in-part of my copendingapplication Ser. No. 859,838, filed Dec. 12, 1977 and pertains to flameresistant styrene-unsaturated polyester resin systems and to a method ofdecreasing the flammability of such styrene-unsaturated polyesterresins.

More particularly, this invention is directed to styrene-unsaturatedpolyester resin compositions prepared by reacting a mixture ofstyrene-polyester resins with diallyl maleate and an alkyl phosphate.

Organic substances containing phosphorus are well known as flameretardants for synthetic plastics, elastomers, fibers, films, etc., aswell as for many naturally occurring combustible substances. Theeffectiveness of organic phosphorus flame retardants varies widelydepending on the base substance but, in general, organic phosphorus isnot known as a highly active flame retardant element for most syntheticresin systems. Frequently, the amount needed to achieve a high level offlame resistance is excessive and the resin matrix is unable toaccommodate the high loading, that is, the resin and high level oforganic phosphorus compounds are incompatible and, in addition, alluseful mechanical properties are lost through modification with theflame retardant.

Where resin modifiers are of limited effectiveness, it is well known inthe art to seek synergists involving combinations of agents to permitthe modifiers to be employed at total concentrations which are less thanfor the individual agents acting alone. Although few synergisticcombinations have been definitely established among flame retardants,one couple, namely, the antimony-halogen combinations, is so widelyemployed that synergism is universally accepted even though there is nogeneral agreement as to mechanism. A similar synergism has recently beenreported for molybdenum oxide and ammonium molybdate in combination withhalogen. (D. A. Church and F. W. Moore, Plastics Engineering 31, No. 12,December 1975). Further, molybdenum oxide combined with antimony oxidereportedly exhibits a synergism vs. the individual oxides when all arecompared in chlorine containing systems.

Synergistic effects with phosphorus are not as readily evident as withthe above metal oxides. Phosphorus plus chlorine generally yields barelyadditive effects. However, it is becoming recognized that phosphorusplus bromine produces synergistic effects in a number of systems.

Enhancement of flame retardant activity by combinations of materials isnot necessarily limited to cases in which both components exerciseactivity individually. For example, in patents to Badische Anilin andSoda-Fabrik Aktiengesellschaft (U.S. Pat. Nos. 3,420,786 and 3,457,204)certain aromatic hydrocarbons of the type2,3-dimethyl-2,3-diphenyl-butane and polymeric isopropylarylenes,respectively, are disclosed as strong activators for organic bromine inflame retardant polystyrene compositions.

Phosphoric acid esters have been used as solvents for flameproofingagents such as pentachlorophenol. The application of such solutions tocellulosic products is described in U.S. Pat. No. 2,926,096.

The fire resistant properties of epoxyalkyl esters of phosphoric acidare taught in U.S. Pat. No. 3,056,806.

U.S. Pat. No. 3,511,857 discloses flame resistant polyester compositionsprepared by reacting a polybasic acid or anhydride with the freehydroxyl groups in the 1,3,2-dioxaphosphorinane ring of phosphonic acid.

Both alkyl and aryl phosphates provide a modest level of flameretardance to styrene crosslinked polyester systems. Oxygen Indexincreases at a rate of about 1.5 units per percent phosphorus present inthe complete formulation. Thus, use of organic phosphates as flameretardants as the sole active constituent has been very limited sincerelatively large quantities are required to attain even a modest levelof flame resistance. Such styrene-containing systems normally employchlorine or, more recently, bromine-containing polyesters which, whensynergized with antimony oxide, can provide a very high level of flameresistance.

In accordance with the present invention, it has now been discoveredthat phosphate esters containing at least one alkyl ester group arerendered much more effective as flame retardants for styrene crosslinkedpolyesters when used in conjunction with diallyl maleate. It isnoteworthy that diallyl maleate in the absence of alkyl phosphate causesonly a slight elevation of the Oxygen Index amounting to approximatelyone unit per ten parts of diallyl maleate added to a hundred of resin.Only alkyl phosphates are so affected although a mixed alkylarylphosphate (octyl diphenyl phosphate) gives similar results as do alkylphosphates having the formula ##STR1## wherein R₁ is alkyl, R₂ is alkylor aryl and R₃ is alkyl, aryl or hydrogen.

The flame resistance of the styrene crosslinked resin composition willvary with the structure of the alkyl phosphate. If a high level of flameresistance is desired (an Oxygen Index of 26 or higher), it is necessarythat sufficient alkyl phosphate be added to the styrene-unsaturatedpolyester to supply an effective amount, from about 0.5 weight percentto as much as about 5 weight percent of elemental phosphorus (P) basedon the weight of styrene-unsaturated polyester.

The diallyl maleate should be added to the styrene-unsaturated polyesterin amounts of about 10 to about 40 parts per hundred.

The ratio of diallyl maleate to phosphorus (P) in thesytrene-unsaturated polyester system may vary within the range of fromabout 2:1 to about 50:1. Particularly preferred is a styrene-unsaturatedpolyester system containing from about 0.6 to 1.8 weight percenttriethyl phosphate and a weight ratio of diallyl maleate to elementalphosphorus in the range of from about 10:1 to 50:1. When the trialkylphosphate is tributyl phosphate, the weight percent phosphorus isdesirably about 0.8 weight percent and the ratio of diallyl maleate tophosphorus is about 37:1.

The invention is further illustrated by the following examples in whichall quantities are given in parts by weight. The Oxygen Index reportedin the Table I is determined by test method D2863-76.

EXAMPLE 1

A styrene-unsaturated polyester system is prepared by dissolving a 1:1maleic-isophthalic acid ester of dipropylene glycol (manufactured andsold by the Diamond Shamrock Chemical Co. under the trade name DIONE ISO6421®) in an equal weight of styrene to form a 50% solution. To 100parts of this styrene-unsaturated polyester solution is added diallylmaleate and triethyl phosphate in the amounts indicated in Table I, and3 parts per hundred of benzoyl peroxide. Each solution is agitated untilhomogeneous, then deaerated and sealed in quarter inch by eight inchglass tubes for curing. Determinations of curing characteristics byDifferential Scanning Calorimetry indicate reaction initiation for thisinitiator-resin combination occurs in the range of 70° to 75° C.Further, samples cured overnight in this temperature range show noresidual energy, i.e., all chemical reactions capable of occurring hadindeed occurred during this thermal exposure. All samples were,therefore, cured by placing the quarter inch specimens (in glass tubing)in a water bath maintained at 70° to 75° C. and heated a minimum of 16hours.

The cured specimens are relatively easily removed from the glass tubesby chilling in ice which, coupled with the contraction during curing,resulted in sufficient shrinkage to cause separation of a solid resinfrom the glass walls. Oxygen Index measurements are then made on the rodspecimens.

Table I lists the results obtained from combinations of diallyl maleatewith triethyl phosphate. When two different Oxygen Indexes are given inthe Table two Oxygen Index measurements were made on the same sample.

                  TABLE I                                                         ______________________________________                                        Styrene-Polyester Systems Containing                                          Triethyl Phosphate-Diallyl Maleate Combinations                               DAM      TEP                    Oxygen                                        (phr).sup.1                                                                            (phr)      P (%)       Index                                         ______________________________________                                        0        0          0.0         19.0                                          10       0          0.0         19.9                                          20       0          0.0         19.8 &                                                                        20.6                                          40       0          0.0         22.2                                          0        5          0.81        22.7                                          0        10         1.50        23.0                                          0        15         2.22        22.7 &                                                                        23.0                                          0        20         2.83        24.8                                          0        40         4.71        23.3                                          10       10         1.38        24.9                                          10       40         4.40        24.9                                          40       10         1.10        32.4                                          40       40         3.67        23.2                                          40       5          0.56        25.2                                          40       15         1.60        20.2                                          30       0          0.0         23.2                                          30       5          0.61        30.4                                          30       10         1.18        26.0                                          30       15         1.71        20.5                                          20       5          0.66        20.5                                          20       10         1.27        20.5                                          20       15         1.84        28.0                                          20       20         2.36        26.0                                          ______________________________________                                         .sup.1 (phr) = parts per hundred of styreneunsaturated polyester.        

I claim:
 1. A flame resistant styrene-unsaturated polyester resincomposition comprising said styrene-unsaturated polyester resin incombination with at least about 20 parts per hundred and no more thanabout 40 parts per hundred of diallyl maleate and at least about 5 partsper hundred but no more than about 20 parts per hundred of triethylphosphate; the total quantity of diallyl maleate and triethyl phosphatepresent in said styrene-unsaturated polyester resin being from 35 to 40parts per hundred when from about 20 to about 30 parts per hundred ofdiallyl maleate are present in said composition and 50 parts per hundredwhen 40 parts per hundred of diallyl maleate are present in saidcomposition; the weight ratio of diallyl maleate to triethyl phosphatebeing such that the oxygen index of said composition is 26 or higher. 2.The flame resistant styrene-unsaturated polyester resin composition ofclaim 1 comprising said styrene-unsaturated polyester resin incombination with about 20 parts per hundred of diallyl maleate and about15 parts per hundred of triethyl phosphate.
 3. The flame resistantstyrene-unsaturated polyester resin composition of claim 1 comprisingsaid styrene-unsaturated polyester resin in combination with about 30parts per hundred of diallyl maleate and about 5 parts per hundred oftriethyl phosphate.
 4. The flame resistant stryene-unsaturated polyesterresin composition of claim 1 comprising said styrene-unsaturatedpolyester resin in combination with about 40 parts per hundred ofdiallyl maleate and about 10 parts per hundred of triethyl phosphate. 5.The method of improving the flame resistance of a styrene-unsaturatedpolyester resin which comprises adding to said styrene-unsaturatedpolyester resin, prior to polymerization from about 20 parts per hundredto about 40 parts per hundred of diallyl maleate and from about 5 partsper hundred to about 20 parts per hundred of triethyl phosphate, thetotal amount of diallyl maleate and diethyl phosphate added to saidstyrene-unsaturated polyester resin being from 35 to 40 parts perhundred when about 20 to about 30 parts per hundred of diallyl maleateare present in said composition and 50 parts per hundred when 40 partsper hundred of diallyl maleate are present in said composition; andheating the mixture to polymerization temperature in the presence of acatalyst; the weight ratio of diallyl maleate to triethyl phosphatebeing such that the oxygen index of said composition is 26 or higher. 6.The method of claim 5 which comprises adding to said styrene-unsaturatedpolyester resin, prior to polymerization about 20 parts per hundred ofdiallyl maleate and about 15 parts per hundred of triethyl phosphate. 7.The method of claim 5 which comprises adding to said styrene-unsaturatedpolyester resin, prior to polymerization about 30 parts per hundred ofdiallyl maleate and about 5 parts per hundred of triethyl phosphate. 8.The method of claim 5 which comprises adding to said styrene-unsaturatedpolyester resin, prior to polymerization about 40 parts per hundred ofdiallyl maleate and about 10 parts per hundred of triethyl phosphate.